Researchers led by Reto Huber of the University Children's Hospital Zurich, found that caffeine intake in pubescent rodents—equivalent to three to four cups of coffee per day in humans—has resulted in reduced deep sleep and delayed brain development.

Both in humans and in rats, the duration and intensity of deep sleep as well as the number of synapses or connections in the brain increase during childhood, reaching their highest level during puberty and dropping again in adult age.

“The brain of children is extremely plastic due to the many connections," says Huber. When the brain then begins to mature during puberty, a large number of these connections are lost. "This optimization presumably occurs during deep sleep. Key synapses extend, others are reduced; this makes the network more efficient and the brain more powerful," says Huber. Over five days, the researchers administered moderate quantities of caffeine to 30-day-old group of rats and measured the electrical current generated by their brains. The deep sleep periods, which are characterized by slow waves, were reduced from day 31 until day 42, i.e. well beyond the end of administering caffeine. The rats that consumed water, the researchers found more neural connections in the brain then in those who drank caffeine.

During puberty, the brain goes through a maturing phase where mental diseases can appear and develop. Although rat and human brains are different, many parallels in how the brains develop raise the question as to whether children's and young adult caffeine intake is harmless or is it wise to abstain from consuming caffeine.

More research is needed to further determine if caffeine and brain development are linked in humans.